One approach to intensive insulin therapy is a continuous subcutaneous insulin infusion utilizing an external insulin infusion pump. The portable pump is connected to the patient via a flexible tube attached at one end to the pump and at the other end to a patch with a needle for subcutaneous injection. The patch typically comprises an adhesive to adhere to the patient's skin. The patch with needle is typically provided with a short section of transparent flexible tube through which the insulin is supplied to the patient, the tube extending from the needle to a connector for connection to a complementary connector at the end of a flexible tube extending from the insulin pump. This enables the patch with needle to be regularly changed, for example every three days. The insulin is supplied in a disposable cartridge with a reserve of insulin that may last for three days to three weeks depending on the patient's insulin requirement. The patch with needle is thus changed more often than the insulin cartridge. At each change of patch with needle or of the insulin cartridge, the flexible supply tube or section of tube must be filled with insulin and any air removed prior to subcutaneous injection. Many precautions must be taken when changing the insulin cartridge, and a rigorous procedure must be followed. There is therefore a risk of false manipulation in existing insulin pump systems, particularly when components are replaced. Risks of errors are increased by the need to change the patch at intervals different to those required for the insulin cartridge.
A further disadvantage of the existing insulin pumps is that, in spite of their portability, they are not sufficiently compact and light to be carried without a certain discomfort and inconvenience. Moreover, the size of the existing insulin pumps does not allow them to be easily positioned close to the point of injection. They thus require fairly long flexible supply tubes, with the disadvantages this confers, when considering the need to evacuate the air from the tubes, and the high cost of the tubes when replacement is needed.
Another important disadvantage of existing insulin pumps is that they are unable to pump very small quantities of liquid with sufficient precision to allow the insulin in the cartridge to have a higher concentration thus enabling a longer interval between cartridge changes and/or reduction in the size of the cartridge. The limited precision of conventional pumps is thus a limiting factor on the miniaturization of the pump and the length of intervals between cartridge changes. The aforementioned factors also adversely affect the portability of the device and the high risk of manipulation error by patients in view of the long supply tubes and the need to change different interconnected elements, such as the cartridge, the flexible tube and the patch with needle. Each connection and disconnection operation requires a procedure to be followed and precautions to be taken by the patient, which are subject to a certain risk of false manipulation.